The present invention relates to a measuring device and method for measuring the crosswise profile of a paper web.
Up to now it has been customary to move the measuring head along the measuring bridge, crosswise to the paper web, with always the same speed. This results in the measurements always taking place in the same time frame at the individual measurement places.
The goal of measuring is to determine the stable cross section of the web and to make corrections to the accumulation of material accordingly, for example by the required adjustment of the inside width of the headbox gap or slice --and along and crosswise to the direction of running--in order to achieve a desired cross section or transverse profile of the web. Formation of the desired cross section of the web is impaired by interference or disturbances in the material flow from the headbox. These interferences, which may result in deviations from the desired cross section, cannot always be precisely determined. It may happen that the frequency of the interference or disturbance and the frequency of measurement are in a whole number relationship to each other. In this case the measurement result may falsely indicate a deviation from the desired cross section. Therefore, a correction as a result of such a measurement cannot lead to the attainment of the desired cross section or transverse profile of the web.
GB-A-1 218 001 discloses a measuring device for determining average values, for example, for the thickness of a passing web. In this connection the sensing speed is controlled proportionally to the speed of movement of the web. However, this measuring system is not capable of preventing the falsification of the results caused by the matching of the measuring frequency and the interference frequency.